By Nam Hyun-wooSK Holdings said Tuesday it has acquired a 270 billion won ($239 million) stake in China's top copper foil maker, becoming the No. 2 shareholder of the producer of the key material for electric vehicle (EV) batteries.According to the holding and investing company of SK Group, its board decided to acquire the stake in Wason, although it did not reveal the exact size, saying it purchased between 25 percent and 30 percent.Copper foil is the core material of secondary batteries and there are only six manufacturers capable of producing it thin enough for EV batteries, and Wason ― which is preparing for an IPO ― is one of them SK holdings said. The holding firm said it decided to acquire the stake as the global copper foil market will see explosive growth amid the increased penetration of EVs. Approximately 40 kilograms of thin copper foil are required for an EV.Wason posted 340 billion won in sales and 62 billion won in operating profit last year. Its yearly copper foil production was 30,000 tons this year and will increase to 75,000 tons by 2022. It is the only copper foil manufacturer to supply all EV makers.